PIPE 1102569 - Caterpillar

Generator Drive System (Off)
Illustration 1 g01189419
When the engine is not operating, the bias piston spring forces the swashplate in the generator pump to the maximum angle. When the engine is started, the pump begins to produce flow. Supply oil is sent to the pressure compensator spool and to the flow compensator spool. These spools are inside the pump. Supply oil is also sent out of port "B" of the pump to port "P" of the generator manifold.When the generator is not operating, the generator control solenoid is de-energized. In this situation, supply oil is blocked at the spool of the generator control solenoid. As pressure increases in the system, supply pressure forces the flow compensator spool to shift against the combined force of the margin spring and signal pressure. This shift sends some oil into the displacement piston cavity causing the pump to destroke. As the swashplate angle decreases, the displacement piston uncovers a passage for oil to flow from the displacement piston cavity and into the pump case.At this point, supply pressure decreases, and the combined force from the margin spring and signal pressure causes the flow compensator spool to shift. This shift closes the passage for supply oil to the displacement piston cavity. As a result, the swashplate angle increases. Eventually, the load sensing spool reaches equilibrium. As a result, the pump operates at low pressure standby. At low pressure standby, the pump produces the flow that is needed to make up for system leakage.Generator Drive System (On)
Illustration 2 g01189424
When the generator switch is in the ON position, the generator control solenoid is energized. Pump supply oil flows through the flow control valve and across the generator control spool. The flow control valve can be adjusted in order to control the frequency of the generator.Downstream from the generator control spool, supply oil is sent out port "LS" to the pump controls. Supply oil is also sent out of port "A" of the generator valve to the generator motor. As the pump supply oil attempts to overcome the restriction of the generator motor, the pressure in the load sensing line increases. The increased signal pressure is transmitted to the flow compensator spool that is in the pump. The increased signal pressure causes the spool to shift. The shift closes the passage for supply oil to the displacement piston cavity. As a result, the swashplate angle increases.The generator motor begins to turn. Generator operation produces power in the high voltage circuits. Eventually, the system reaches equilibrium. At this point, the pump flow is held at a level which is adequate to fulfill the system load and the system flow requirements.If the signal pressure reaches the setting of the pressure compensator spring, the pressure compensator pilot valve opens. When this valve opens, the load sensing pressure is limited. This action causes the pump to destroke until equilibrium is again established.